On April 18, 1983, Ryan Crocker was in his office at the U.S. Embassy in Beirut, with its spectacular view overlooking the Mediterranean. His wife, Christine, was working next door. At 1:05 p.m. a dark delivery van made a sharp left onto the guarded cobblestone lane and rammed into the front wall, detonating an explosive that ripped apart the seven-story high-rise. A huge brown cloud of smoke could be seen for miles.

It was the first suicide bombing by Islamic extremists against a U.S. target.

Crocker -- the career diplomat the Bush administration has nominated to serve as U.S. ambassador in Baghdad -- was blown against the wall. Bloodied but not seriously injured, he and his wife fled the building. He then began to search through the twisted steel and concrete for colleagues.

New York Times correspondent Thomas Friedman lived nearby and raced to the site. "I came around the corner and there was the American Embassy cut in half like a doll's house, bodies hanging out of it, smoke belching, and the first person I saw staggering around in the ruins was Ryan, his sleeves rolled up, looking in the rubble," Friedman recalls.

The bomb, which killed 64 and wiped out the CIA station, marked the start of a trend that now defines U.S. foreign policy.

If there's an awful assignment in the Middle East or South Asia, Crocker, 57, has had it. He actually prefers the hot spots, colleagues say.

The toughest hardship assignment for Crocker -- and the only one he tries to avoid -- is Washington, says former ambassador Edward Abington. "He prefers the most difficult posts. There's a real sense of adventure in him," Abington says.

Seven months before the Beirut attack, I encountered Crocker after a right-wing Christian militia entered the Beirut slums of Sabra and Shatila and, in a 48-hour orgy of killing, murdered some 800 people, including many women, children and the elderly. Journalists were among the first to go into the area after the militia left, but when many of us arrived, Crocker and his wife were already surveying the bloodshed and streets littered with bodies.

"With a hand-held transmitter, he was walking through the Shatila refugee camp and describing as he moved scenes of a massacre of shocking magnitude," wrote former secretary of state George Shultz in his autobiography, "Turmoil and Triumph."

The massacre followed the assassination of Lebanon's Christian President-elect Bashir Gemayel.

"I was on the phone with him for hours trying to confirm whether or not Gemayel was dead," recalls former U.S. assistant secretary of state Elizabeth Jones. "We had been burned with the [former Egyptian president Anwar] Sadat assassination, so we had to have someone see the body or say that he was still alive."

Crocker was dispatched. "He's extremely tough-minded about what needs to be done even in the worst tragedy," Jones says.

He now appears headed to Baghdad as part of a personnel sweep that is bringing a whole new set of faces to the top of diplomatic and military jobs as part of President Bush's "new way forward" in Iraq.

For Crocker, an Air Force officer's son who attended schools in Morocco, Turkey and Canada, it's coming full circle.

He first went to Baghdad as a young economic officer, a year before Saddam Hussein seized power in 1979. Baghdad had broken off relations with Washington, so the United States had an interest section. U.S. diplomats were under 24-hour surveillance and banned from leaving Baghdad without government permission.

"It was very difficult to make contact with Iraqis, as it was so dangerous for them," says Jones, who was posted in Baghdad as political officer. "Saddam executed most of his first cabinet, so we already knew what a difficult person we were dealing with. . . . Ryan was the best at triangulating the situation and figuring out what was happening."

Iraq then invaded Iran in 1980, setting off the bloodiest and longest modern Middle East war. Crocker and Jones had to evacuate Americans, but stay themselves.

Crocker met and married his wife, Christine, a foreign service secretary, in Baghdad. The two have been inseparable ever since, colleagues say.

Almost a quarter-century later, Crocker was one of the most significant voices inside the administration about the dangers of invading Iraq.

In late 2002, as the Bush administration prepared for war, then-Secretary of State Colin L. Powell tasked Crocker and Assistant Secretary of State William Burns with exploring the risks of military intervention. The result was a six-page memo they entitled "The Perfect Storm," according to an account in Washington Post reporter Karen DeYoung's biography "Soldier: The Life of Colin Powell."

The memo bluntly predicted that toppling Hussein could unleash long-repressed sectarian and ethnic tensions, that the Sunni minority would not easily relinquish power, and that powerful neighbors such as Iran, Syria and Saudi Arabia would try to move in to influence events. It also cautioned that the United States would have to start from scratch building a political and economic system because Iraq's infrastructure was in tatters.

Crocker returned to Iraq after the 2003 U.S. invasion to help during the transition and the creation of the Coalition Provisional Authority. He left that July, a time when he and colleagues could still drive to farewell meetings in the capital in unarmored vans.

The night before he left, Jalal Talabani, the Kurdish leader who is now Iraq's president, threw a large and raucous party for Crocker, who told colleagues in frustration that he was returning to Washington to teach at National Defense University for a year and then retire.

"He has often been critical of policies he has been charged with implementing and had little success in persuading the political leadership to change," says a former colleague who requested anonymity in light of the new appointment.

Iraq will be his fifth embassy as ambassador -- sixth if you count reopening the embassy in Afghanistan after the United States ousted the Taliban in 2001. He also was the top U.S. envoy in Lebanon (again), Syria, Pakistan and Kuwait. Each has involved personal danger or crisis.

In 1998, during a U.S. bombing campaign on Iraq, Syrian mobs attacked the U.S. ambassador's residence in Damascus. Christine Crocker fled into a vaulted safe-room in the residence as rioters ransacked the building. Jones remembers talking to Christine on a line that connected directly to Washington from the residence and on a separate phone to Ryan, who had raced home to help his wife but was stuck outside. The place was so badly trashed that they had to move out.

Though President Bush gave him the State Department's most prestigious title of "career ambassador" in 2004, Crocker is little known outside diplomatic circles and intensely private -- a stark contrast to the flamboyant and media-ready current ambassador to Iraq, Zalmay Khalilzad. Crocker is also an unassuming diplomat in a profession known for its dapper suits and fancy dress.

He drove a pickup truck in Washington, and Crocker coined the term "no socks required" to describe attire at parties he and his wife host.

David Mack, a retired diplomat who served with Crocker in Iraq and Lebanon, still remembers dinners of "cold Spam and peas eaten with crackers" when he stayed at the Crockers' Beirut apartment.

Crocker gets through most of his tough assignments by running. The day before the embassy blew up in Beirut in 1983, he ran in the first -- and some say only -- marathon held in Lebanon. Mack, now vice president of the Middle East Institute, recalls how Crocker took him out running along Beirut's seafront Corniche, during the middle of the civil war.

Crocker has now run in marathons on four continents, including a 50-kilometer race in Jordan. He also ran a 10-kilometer uphill race to the top of Mount Hermon in the Golan Heights that was particularly painful, he told colleagues. As a young foreign service officer learning Arabic, he had to take a field trip to use the language, and he chose to live with a Bedouin tribe of sheepherders in Jordan. He made that choice so he could run, according to Frederic C. Hof, who still remembers Crocker's field report.

In his current post in Pakistan, Crocker still regularly runs, often exhorting members of the embassy staff to join him. "His idea of unwinding is running 10 miles with security guys behind him in a four-wheel drive trying to keep up," says retired Gen. Barry McCaffrey, who has known Crocker for years and recently visited him in Pakistan. Crocker's favorite run is from outside Islamabad to the border of the Northwest Frontier Province.

During the few times he lived in Washington, Crocker ran most days from Alexandria to the State Department, his clothes in a backpack.

Friends say they can always tell when he's worried about something because he runs longer and harder, getting rail thin in the process.

Crocker is the first career foreign service officer and Arabist to take the Baghdad job, which may put him at a disadvantage in persuading the administration on policy. The three previous U.S. envoys -- Khalilzad, Director of National Intelligence John Negroponte and Coalition Provisional Authority chief L. Paul Bremer -- had all been political appointees who had a direct line into the White House.

"It's going to be a terrible job," says former ambassador to Lebanon Robert Dillon, who was also in the embassy when it blew up. "As a career guy, he's going to be under a lot of pressure and I'm not sure how much support he'll get in Washington."

But diplomats and military officers who have served with him say Crocker, who knows Iraq's tribes as well as its Arabic dialect, was the only realistic choice to deal with the country's labyrinthine politics.

Says Abington, "To the extent anyone can make a difference there, Ryan will."